Field of the Invention
This invention relates generally to a flexible fuel hose with low permeability to fuels, and more particularly to a hose with a barrier layer of a particular type of polyamide 6.
Description of the Prior Art
The increased used of motor-vehicle fuels containing alcohol, including ethanol, along with stringent emissions standards for fuel system components has necessitated improvement over conventional flexible hose constructions. Conventional fuel hose constructions used economical, fuel-resistant rubber materials such as nitrile rubber (NBR), nitrile-polyvinyl chloride blends (NBR-PVC), epichlorohydrin (ECO), and the like. Improved hose for alcohol-containing fuels now generally use one or more of various fluoroelastomers and/or fluoroplastics such as those commonly designated as FKM, PVDF, ETFE, FEP, EFEP, PCTFE, THV, PTFE, and the like (hereinafter referred to generally as fluoropolymers) to provide a barrier to alcohol and fuel permeation. The typical preferred material for a fuel hose barrier layer is a fluoropolymer film such as THV (a terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride) an example of which is disclosed in U.S. Pat. No. 5,679,425.
While fluoropolymer barrier hose has dominated the fuel hose market, many other materials are available as potential barrier layers. U.S. Pat. No. 6,945,279, which is directed to a method of making rubber hoses with an intermediate thermoplastic layer by rolling a planar resin film into a cylindrical layer with an overlap, discloses extensive lists of potential rubber materials and thermoplastic resin materials. While NBR is mentioned on the list of potential rubber materials and polyamide 6 (“PA 6”) as a potential resin film, U.S. Pat. No. 6,945,279 offers no particular guidance for selecting materials for any particular use, and no working examples are disclosed therein. Typical fuel hoses have further included multi-layer barrier constructions which combine fluoropolymers with other materials including for example polyamides. Frequently polyamides are cited as useful materials for thermoplastic multilayer tubing for fuels.
An example of use of a thermoplastic film layer of nylon 11 (i.e., polyamide 11) in fuel hose is provided by U.S. Pat. No. 6,279,615, wherein the polyamide (“PA”) is the innermost veneer layer on the inner surface of the rubber hose of a comparative example. Regardless, the permeation rates obtained for the hose described in U.S. Pat. No. 6,279,615 were not low enough to meet current SAE (Society of Automotive Engineers) standards. U.S. Pat. No. 2,564,602 discloses a rubber hose with an intermediate layer of flexible, resinous, thermoplastic material including nylon. U.S. Pat. Pub. No. 2007/194481A1 discloses a rubber hose with inner tube and outer cover of rubber and an intermediate barrier resin layer of any kind of thermoplastic resin including PA 6, but preferably of fluoropolymer for fuel hose applications, wherein the resin layer is plasma treated. U.S. Pat. No. 7,478,653 discloses a 4-layer rubber fuel hose with a barrier layer of fluoropolymer or polyamide (including PA 6).
U.S. Pat. No. 6,855,787 discloses thermoplastic fuel transfer tubes based on polyamide resin, such as PA 6, containing a barrier layer of fluoropolymer. U.S. Pat. No. 6,491,994 discloses a thermoplastic fuel transfer tube based on layers of PA 11 or PA 12 resin, PA 6, and PA 6 with a layered silicate dispersed therein. U.S. Pat. No. 7,011,114 discloses a thermoplastic fuel transfer tube based on polyamide resin containing a barrier layer of polyphenylene sulfide (“PPS”).
An example of use of a multi-layer barrier is disclosed in U.S. Pat. No. 5,038,833, wherein the primary application is rigid plastic pipes. An example of use in a refrigerant hose of a thermoplastic barrier layer is provided by U.S. Pat. No. 6,941,975, wherein the barrier layer requires two or three layers, including a layer of vinyl resin such as ethylene-vinyl alcohol copolymer (“EVOH”) and outer layers of polyolefin and/or polyamide resin. Each resin layer has a thickness of from 0.025 to 0.25 mm. The only example provided in U.S. Pat. No. 6,941,975 used a 3-layer barrier with 0.15-mm total thickness and had a permeation rate for R134 refrigerant of 3.94×10−5 g/cm/day based on a one-cm length of hose of undisclosed diameter. U.S. Pat. No. 7,504,151 discloses a refrigerant hose with a barrier layer of PA 6/66 copolymer, PA 11, PA 12, PA 6, or PA 6/12 compounded with nanofillers. U.S. Pat. No. 7,478,654 discloses a refrigerant barrier hose with a 2-layer barrier that includes as one of the layers a thermoplastic resin such as PA 6 or one of many others.
Reference is made to co-pending U.S. patent application Ser. No. 11/938,139 filed on Nov. 9, 2007, the entire contents of which are hereby incorporated herein by reference. That application discloses a flexible fuel hose having a non-fluorinated rubber inner tube, a non-fluorinated rubber outer cover, an intermediate barrier layer consisting essentially of EVOH having an ethylene content less than 30 mole %, and preferably a textile reinforcement between the barrier layer and the outer cover. A non-fluorinated rubber tie layer may be included between the barrier and the reinforcement. Permeability to ethanol- and methanol-containing fuels is very low. The EVOH layer may be extruded onto an unvulcanized rubber inner tube and an unvulcanized rubber outer cover extruded thereon. However, during handling of the resulting raw hose before and during vulcanization, the stiffness of the EVOH layer can result in kinking, delamination and other processing problems. As a result of this stiffness, EVOH-based hose failed the SAE J30R14 kink test.